As is known in the art, “space-based” systems refer to space-borne systems that may have any of a variety of different purposes. A space-based radar, for example, refers to space-borne radar systems which may be used for object detection or other purposes. Similarly, space-based communication systems refers to space-borne communications systems. In telecommunication, a communications system is a collection of individual components such as communications networks, transmission systems, relay stations, tributary stations, and data terminal equipment (DTE) usually capable of interconnection and interoperation to form an integrated whole. Thus, a space-based communication system refers to a communication system in which at least some components are space-borne.
As is also known, a difficult challenge for space-based systems including space-based communication systems is minimizing size, weight and power (SWAP). Some space-based communication systems utilize space-based optical phased arrays (OPAs). In OPA systems, light controlling elements (e.g. spatial light modulators also referred to as OPA elements) are used to steer or aim light beams (e.g. laser beams), or steer or aim sensors, by progressive phase modulation.
OPA systems generally include an OPA aperture provided from a plurality of such OPA elements. In general, OPA elements are limited in size due to manufacturing limitations related to patterning or otherwise providing electrodes on a liquid crystal device or other substrate. To create relatively large apertures, a modular approach is used in which each of a plurality of OPA elements are disposed in individual support/alignment frames to provide framed OPA elements. The framed OPA elements are arrange in groups (or “tiled”) in desired patterns to form an entire OPA array.
The use of tiling techniques in such a modular approach, however, introduces multiple problems. One problem is the frame which is used to hold (or support) and align each OPA element adds weight and size to the array of such OPAs which form the OPA aperture. In addition to the added size and weight resultant from using such support/alignment frames, light does not efficiently propagate through the support/alignment frames. Thus, the support/alignment frames cause a blockage in the array aperture which among other things, reduces gain and increases signal loss of the aperture.
To compensate for increased signal loss and reduced gain due to such aperture blockage by the OPA frame structure, it is necessary to increase the size (and consequently the weight) of the OPA aperture. Furthermore, the frames cannot be manufactured with tolerances which ensure alignment of the OPAs with the requisite accuracy. Thus, it is necessary to add so-called adjustment features to the frames. The adjustment features are mechanical devices which can be manipulated to mechanically align t the OPA elements. However, such adjustment features add further weight to the frames.
Yet another problem with OPA apertures relates to non-symmetrical thermal gradients caused by conventional modular OPA aperture designs in which control electronics of each OPA element are coupled to only one side of each OPA element. Such asymmetrical thermal gradients can significantly affect wave front distortion error. To compensate for such asymmetrical thermal gradients, additional heaters and thermal material are sometimes added to each OPA element. This results in a still larger and heavier OPA aperture. Thus, as can be surmised from the above, the modular structure of conventional OPA apertures comes at the cost of additional SWAP due to additional structure added to each individual OPA element.
In general, prior art approaches to solving the above problems have focused on minimizing the size and weight of the frame and related structures supporting each OPA element. Such approaches, however, are limited to practical sizes in the 3 mm range since frames below 3 mm in thickness are generally unable to provide sufficient structural support for the OPA element. Also, lightweight heaters have been used to manage the problems with thermal gradients but at the cost of additional SWAP.